This invention relates to decreasing the flammability of halogen-containing polymer compositions.
It is well known that the flammability of synthetic organic polymers can be significantly reduced by including a halogen source in the polymer composition. Among the preferred halogen sources are halogen-containing hydrocarbons, particularly bicyclic hydrocarbons such as perchloropentacyclodecane. Alternatively, the polymer itself can function as the halogen source. Examples of the latter are polyvinyl chloride and other polymers derived from halogen-containing monomers.
In addition to reducing flammability of synthetic polymers it is also desirable to reduce the amount of smoke generated during combustion, since in many instances the dense, toxic smoke presents as much, if not more, of a hazard than the fire itself.
A number of zinc compounds, including zinc oxide and zinc sulfate have been proposed as flame retardants for various types of polymers, however these compounds are less than desirable because they adversely affect the heat stability of the polymers.
It is therefore an objective of this invention to define those zinc compounds which act as flame retarding agents and smoke suppressants without adversely affecting the heat stability of halogen-containing polymers and polymer compositions containing an organic halogen source. Surprisingly it has been found that zinc sulfide, a relatively inexpensive zinc compound, achieves this objective.